1. Field of the Invention
The present invention relates generally to a traffic signal device constructed in accordance with the coloring phenomenon of optical thin films. Theoretically, the color performance of optical thin films is based on the phenomenon that waves reflected from interfaces of different depths interfere with each other. The present invention adapts such an optical principle to make use of the wave interference of a multilayer coating to increase the intensity of a specific wave length so as to display a desired color. Further, due to the fact that the spectra of the red light, the yellow light and the green light are substantially not overlapped by each other, a particularly designed thin films configuration may reflect and thus display red signal, yellow signal and green signal from a white light beam to provide the required traffic signals of different colors.
2. Description of the Prior Art
Conventional traffic signal devices comprise a housing inside which at least a red signal unit, a yellow signal unit and a green signal unit are mounted. The housing is supported by a frame which is usually located on the intersection of roads or streets. Each of the signal units comprises an illuminating source or a lamp secured within a parabolic reflector with a hood lens made of colored, light-transmittable plastics or glass disposed in front thereof. Such a prior art arrangement requires at least three lamps for a complete set in a traffic signal device which usually includes at least a red signal, a yellow signal and a green signal. The power consumption of one of such lamps is generally between 69 to 135 watts each lamp, depending upon the required brightness of the signals. The consumption of electrical power is one of the major costs of the traffic signal device.
Further, there are other shortcomings of the conventional traffic signal device. For example: (1) sun light which is incident onto and through the hood lens and reflected by the parabolic reflector will imitate the normal lighting of the traffic signal and creating a phantom image which very probably leads to traffic accidents; this is the well-known sun phantom effect; (2) the switching between different signals requires that the associated lamps be turned off/on frequently which not only consumes more power but also shortens the service life of the lamps and as a consequence, maintenance and replacement cost of the lamps increases and traffic control becomes more difficult due to the temporary shut down of the lamps in maintenance and replacement; and (3) the large amount of heat generated by the lamps and the radiation of sun light deteriorate the colored hood lens and the color thereof fades and as a result, the traffic signals projected therethrough becomes pale and weak.